1. Field of the Invention
The present invention relates to a laser processing apparatus that performs laser processing such as cutting or welding of a workpiece by applying a laser beam to the workpiece.
2. Description of Related Art
There are known laser processing apparatuses that perform laser processing such as cutting or welding of a workpiece by applying a laser beam to the workpiece. Some of the laser processing apparatuses are provided with a processing head including a head main body and a nozzle. The head main body houses an optical system including, for example, a condenser lens that a laser beam from an optical fiber enters and that condenses the laser beam. The nozzle applies the laser beam to the workpiece. Protection glass that protects the optical system from, for example, spatters generated during laser processing is disposed on the nozzle side of the optical system. Air or assist gas is supplied into the nozzle. By injecting the air or assist gas from the nozzle, spatters, fumes and the like generated by laser beam application are removed from a laser beam application portion. For example, Japanese Patent Application Publication No. 2012-24831 (JP 2012-24831 A) describes such a laser processing apparatus including protection glass that protects an optical system housed in a head main body of a processing head, and a nozzle into which air or assist gas is supplied.
In the laser processing apparatus described in JP 2012-24831 A, a processing head 27 is formed by coupling a blow nozzle 52 (nozzle) and a lens holder 51 (head main body) together by thread fastening, with a protection member 75 (protection glass) installed on the blow nozzle 52, and the protection glass is disposed between the lens holder 51 and the blow nozzle 52. The blow nozzle 52 has a supply passage 72 through which air flows. The air is supplied to a nozzle hole 73 of the blow nozzle 52 through the supply passage 72, and the supplied air is injected from the nozzle hole 73 toward a laser processing point.
In the processing head 27, a distal end portion of the lens holder 51 is housed in a housing space formed in the blow nozzle 52, and a clearance, which serves as an internal passage 71, is formed along the entire circumference between the inner peripheral surface of the blow nozzle 52, which defines the housing space, and the outer peripheral surface of the lens holder 51. The internal passage 71 communicates with the supply passage 72 and the nozzle hole 73. The air supplied to the supply passage 72 flows through the internal passage 71 and is then injected from the nozzle hole 73 toward a laser processing point. In this case, the air supplied to the supply passage 72 cleans the protection member 75 by flowing along the lower surface of the protection member 75 when flowing from the internal passage 71 into the nozzle hole 73.
In the processing head 27, however, sealing is not provided between the protection member 75 and the lens holder 51 and thus airtightness inside the lens holder 51 cannot be maintained. Thus, spatters, fumes and the like generated by laser application may enter the lens holder 51 from between the protection member 75 and the lens holder 51. This makes it difficult to keep the inside of the lens holder 51 clean. The blow nozzle 52 is fastened to the lens holder 51 by thread fastening. However, the thread-fastened portions may come loose due to, for example, vibrations during the operation of the processing head 27. This may further reduce the airtightness between the protection member 75 and the lens holder 51.